I am fortunate enough to have a small stash of Toshiba Jfets and am wondering about which amps are good for which idss level. I have read where a few of these amps are preferring certain idss, others are good for a range.
I have several sets in the 7.5 range, and a few in the 8.0 range. I figure these are sweet for most Pass applications? please advise if some may not favor this measurement, but my understanding is that this is a sweet spot, and what I have generally used for my builds here.
Then I have an octet of them at 8.4, which I was tenatively saving for a pair of BBA3 mono blocks. Are there any Pass amps these may not be good for?
Lastly, I have some several sets at 9.4. These concern me the most, getting a little high. Are there Pass projects these are not suited to?
I have also read where adjustments can be made to allow for less than perfect idss ranges, like F5, I remember some members having to make a resistor change to get sufficient range on the adjustment pots, etc.
Basically, I want to organize the last of my Jfets, saving the best for projects that merrit them, and the others for projects where adjustment isnt critical.
Maybe I am wrong, but I suspect the 8.4 are probably OK, but have doubts about the 9.4-9.5 ones....
Any thoughts would be appreciated, I want to parse these out over my building years, until more LS units are available, or different ones like Mark and Zenmod have utilized in their projects.
Thanks in advance,
Russellc
I have several sets in the 7.5 range, and a few in the 8.0 range. I figure these are sweet for most Pass applications? please advise if some may not favor this measurement, but my understanding is that this is a sweet spot, and what I have generally used for my builds here.
Then I have an octet of them at 8.4, which I was tenatively saving for a pair of BBA3 mono blocks. Are there any Pass amps these may not be good for?
Lastly, I have some several sets at 9.4. These concern me the most, getting a little high. Are there Pass projects these are not suited to?
I have also read where adjustments can be made to allow for less than perfect idss ranges, like F5, I remember some members having to make a resistor change to get sufficient range on the adjustment pots, etc.
Basically, I want to organize the last of my Jfets, saving the best for projects that merrit them, and the others for projects where adjustment isnt critical.
Maybe I am wrong, but I suspect the 8.4 are probably OK, but have doubts about the 9.4-9.5 ones....
Any thoughts would be appreciated, I want to parse these out over my building years, until more LS units are available, or different ones like Mark and Zenmod have utilized in their projects.
Thanks in advance,
Russellc
All of them are right in the butter zone! 🙂 Use them in any project without worry, they will work perfectly!!
That's good to know, I was afraid the higher ones would need some sort of attention to work.
Thanks,
Russellc
Thanks,
Russellc
yup , what Jim sez
and even more generally - those with higher Idss are perfectly good when biased through CCS ( as in Aleph J or J2 , situated in LTP) , or biased with voltage reference (as in ACA or SIT-1,2 )
and even more generally - those with higher Idss are perfectly good when biased through CCS ( as in Aleph J or J2 , situated in LTP) , or biased with voltage reference (as in ACA or SIT-1,2 )
In general you're fine. I've ued 9+mA Idss 2sk170/2sj74 in my builds and
they work as expected. On ZM's point about CCS, my AJ uses even Idss
parts (2sj108V) and works very well.
Often it's lowish Idss / high Vgs output devices that requires a bit of
resistor adjustment.
The one project I can think of off the top of my head where high idss is not
recommended is the F5 Turbo V1 without cascoding, where the combination
of higher current and rail voltages can push the jfets pass their thermal limits.
Cheers,
Dennis
they work as expected. On ZM's point about CCS, my AJ uses even Idss
parts (2sj108V) and works very well.
Often it's lowish Idss / high Vgs output devices that requires a bit of
resistor adjustment.
The one project I can think of off the top of my head where high idss is not
recommended is the F5 Turbo V1 without cascoding, where the combination
of higher current and rail voltages can push the jfets pass their thermal limits.
Cheers,
Dennis
Yes, I think in the early F5 days, many had low idss parts that required a resistors change. Seems like I remember F6 needing a little lower idss when I built it? That's been a while.
Russellc
I used 9-ish mA for my F6 and didn't run into any issues.
I'm sure the parts you have will serve you well.
Cheers,
Dennis
I'm sure the parts you have will serve you well.
Cheers,
Dennis
My F6 using 8'ish NP matched, and BA3FE uses 10mA matched.
Sadly my Jfet supplier went uncontactable now !
Sadly my Jfet supplier went uncontactable now !
No no no
They're all hopeless. Please send to myself for correct disposal, and I'll send you some lovely op-amps for all your amps front end needs.
:Crosses fingers and wanders away whistling:
They're all hopeless. Please send to myself for correct disposal, and I'll send you some lovely op-amps for all your amps front end needs.
:Crosses fingers and wanders away whistling:
I have a set of the stores LS version, but have no idea there idss. Spencer at fet audio listed some sets still, but I think they were around 10 idss.
I just checked looks like he has 9.5 to 11 idss still. His are good to go.
Russellc
I just checked looks like he has 9.5 to 11 idss still. His are good to go.
Russellc
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I have some matched 2sk170BL as well as a few 2sk170/j74 pairs/quads and some bags with 20-40 2sk170BL sorted into the 9-10 idss ranges that I thought of trying to get some j74 to match to.
I’m sure this has been asked before, but I can’t remember the answer. What is the minimum and maximum cut off point concerning idss when considering use in the majority of the FW DIY amp designs?
Is it possible to use 2sk170/j74GR pairs in any of the designs that might fall into the 6 idss range?
I’m sure this has been asked before, but I can’t remember the answer. What is the minimum and maximum cut off point concerning idss when considering use in the majority of the FW DIY amp designs?
Is it possible to use 2sk170/j74GR pairs in any of the designs that might fall into the 6 idss range?
Maybe only a little luck. As it is there are too many FW amps I still want to try and too few dodofets...and the sources you can find just keep jacking the prices up on what they have left.
I recently finished a scaled down version of Pa’s SLOB I put aside a while ago. After playing with my UMIK-1 and REW for the first time it’s become apparent that they are much further behind my Oris horns than I thought they might be. Not as bad with Fostex 206e as with Lowther DX3.
I was hoping a standard F5 would be a good choice for these dipole bass panels. I’m not convinced I could pull that off without at least a Turbo V1. The low idss fets might be handy for that. Unfortunately, it seems there’s no pcb readily available without going for a V2 or V3.
Has anyone tried socketing in the jfets so they can be easily removed for reuse?
If that's a bad idea, maybe leaving the leads long when you solder them?
You should be able to build F5V1 using the V2 boards, by leaving out some
parts and maybe adding jumpers.
Dennis
If that's a bad idea, maybe leaving the leads long when you solder them?
You should be able to build F5V1 using the V2 boards, by leaving out some
parts and maybe adding jumpers.
Dennis
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Basically anything in the BL range, I.E., 6-12mA. It's really not that critical. 7-9mA is probably "ideal", HOWEVER, it's also the center of the distribution and the most common. 🙂
Yes there is -
Leave the diodes off the output boards. That's a V1. Include the diodes and it's a V2. Add more output boards and it's a V3
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